The chick starts out as a single cell that divides and forms a hollow disc on the surface of the yolk. This yolk is then released into a spiralling oviduct tube. As it travels down the oviduct it builds up a number of layers, including a vitelline membrane directly surrounding the yolk, and two layers of viscous white albumen divided by a structural fibrous layer. Lower in the oviduct tube the eggshell layer develops around the yolk, protecting it and giving it form. When the egg is expelled from the body so begins the following 21-day period of embryonic development…